1. Field of the Invention
This invention relates to ion-exchange materials and is particularly concerned with sulfonated cellulose which is activated and has large surface area, and sulfonic acid salt derivatives thereof, having ion-exchange properties, and with cost-effective processes for the preparation and use of such materials. The products have particular utilities in efficiently and economically removing heavy metal ions from aqueous solutions, for example in the treatment of industrial and municipal effluents, and in precious metal recovery.
2. Description of the Related Art
Ion-exchange compositions consist of cross-linked, high polymeric structures to which are attached ionizable groups. Cation-exchange properties arise due to the presence of one or more functional groups on the polymeric matrix, such as the strongly acidic sulfonic acid functionality (--SO.sub.3 H), the weakly acidic carboxylic acid functionality (--COOH), or the very weakly acidic phenolic functionality (--OH).
The phenomenon of ion-exchange was first reported by two British agricultural chemists in 1850, who proved that soil can remove potassium or ammonium salt from water with the release of an equivalent amount of the calcium salt. Adams and Holms used ion-exchange resins consisting of a three-dimensional network of polymeric chains crosslinked with short chain-containing ionizable fictional groups. By the proper use of these ions, it is possible, in principle, to replace any ion in a solution by another ion of like charge by an ion-exchange process in which ions in the solution are exchanged with the ions in the resin.
The classic ion exchange studies of Gans are probably the first attempts to utilize ion exchangers for industrial purposes. Gans employed both natural and synthetic aluminum silicates for softening waters and also for treating sugar solutions. Although alumino-silicates are widely used in water treatment and other fluid purification and treatment applications, they typically are limited in achieving satisfactory results to processes under nearly neutral conditions, in which the pH ranges from 6.5 to 7.5. This problem was later solved with the development of sulfonated coal as a cation exchange. Adams and Holmes observed that certain synthetic resins are capable of exchanging ion. They found, for example, that crushed phonograph records are capable of exchanging ions. They further established that stable and high capacity cation exchanger could be obtained using sulfonic acid resins and that polyamine type resins exhibited good anion exchange properties. The pioneering work of Adams and Holmes was followed by D'Alelio in the U.S. which led to the synthesis of ion exchange resins derived from styrene and the acrylics.
D'Alelio's synthesis of sulfonated copolymers of styrene and divinylbenzene yielded strong acid resins. I. G. FarbenIndustrie synthesized phenol-fomaldehyde resins with sulfonic groups attached to the rings through methylene groups.
Against this historical background, there is a continuing research and development effort directed to the synthesis of new cationic and anionic ion exchanger materials.
Cellulose is the most important structural component in plants and is present mainly in the cell wall. Yckel and Kenyan showed that oxidation of primary-alcohol groups in cellulose produces a weak acid cation-exchanger. Sober and Peterson investigated the preparation and properties of cellulosic ion exchangers, work which was extended by Porath and Somenza. Peterson worked on biologically active poly-electrolytes and determined their net charge characteristics.
A number of ion-exchanger materials are commercially available, which include, by way of example, oxycellulose, cellulose succinic esters, and a variety of treated cotton fabrics. Peterson and Sober prepared cellulose ion-exchange materials by the reaction of a chloro-compound with cellulose which had been allowed to swell in a strong alkali.
Other research approaches to the development of cationic ion exchange materials include the bonding of cation-exchanger compositions to microporous silica. Such compositions may be subjected to functionalizing reactions to introduce different ionic functional groups into the bound cation-exchange material.